Human Relatives Were Butchering and Eating Each Other 1.45 Million Years Ago

Scientists have discovered the oldest evidence that early relatives of humans butchered, defleshed, and probably ate each other, according to a new study that identified cut marks on a shin bone that dates back 1.45 million years to northern Kenya. 

The nine marks on the ancient fossil appear to have been made with a stone tool during the process of cleaving meat from the bone, possibly for consumption. Though older traces of butchery have been reported on an ancient skull, the cut marks are by far the earliest unambiguous sign that close members of our human family used tools to deflesh the bodies of their relatives.

Humans are the only surviving members of a much larger family of “hominins” that emerged in Africa millions of years ago. There is plenty of evidence that various hominins slaughtered and devoured their close relatives over the past few hundred thousand years, but the origin of this behavior becomes murkier once the fossil record reaches into the Early Pleistocene period, which occurred between 800,000 and 2.5 million years ago. 

Now, researchers led by Briana Pobiner, a paleoanthropologist at the Smithsonian National Museum of Natural History, have presented “the first (and to date only) cut marks identified on an early Pleistocene postcranial hominin fossil,” where “postcranial” means any fossil that is not a skull, according to a study published on Monday in Scientific Reports.

After thorough examination of cut marks on the ancient shin fossil, which is known as KNM-ER 741, the researchers concluded that if the leg flesh was consumed by a hominin species, it was likely “an opportunistic, practical, and functional activity which occurred simply in the context of obtaining food, rather than one imbued with ritual meaning,“ the study said.

“The biggest implications of the antiquity of hominins butchering other hominins is the idea that our ancient relatives nearly 1.5 million years ago, at least on occasion, may have viewed other dead individuals as possible food sources,” Pobiner told Motherboard in an email.

She also noted that there is an even older hominin skull from South Africa, known as Stw 53, that may have signs of butchery on its cheekbone, but that the marks identified by her team on KNM-ER 741 are “the oldest defleshing marks” in the fossil record. Furthermore, Pobiner added that the interpretation of the marks on Stw 53 were challenged by a 2018 study that suggested they could have been made by trampling, casting some doubt about their origin, whereas the the marks on KNM-ER 741 are almost certainly evidence of butchery.

Indeed, the cut marks on the shin bone are so unusual that they immediately caught Pobiner’s eye when she came across them in July 2017 at the National Museums of Kenya’s Nairobi National Museum. Pobiner was examining the museum’s hominin fossils in search of damage inflicted by carnivores, such as saber-toothed cats, that may have hunted and killed our early human relatives in this bygone era. 

While KNM-ER 741 appears to have a few bite wounds from a big cat, it is also etched with several neat lines oriented in the same direction, a pattern that strongly suggests the marks were made by stone tools. The cuts are also located along a calf muscle that was attached to the bone, making it a convenient place to remove flesh from a body.

“I have studied hundreds of fossil animal bones with cut marks on them, but this was my first time studying fossil hominin bones—expecting to possibly find predator bite marks,” Pobiner recalled. “So, as soon as I saw the cut marks, it was immediately clear to me what they were. I thought ‘whoa, that’s not what I was expecting to see!’”

Impressed by the specimen, Pobiner sent molds of the cuts to study co-author Michael Pante, a paleoanthropologist at Colorado State University who specializes in feeding behaviors of early hominins, without giving him any information about the source fossil. After a comparative analysis of nearly 900 damage marks created in experiments, Pante confirmed the lines were very likely made during the defleshing of a corpse using stone tools. 

While the researchers think it is likely that the butchered carcass was consumed for nutrition, this is not a clear case of cannibalism in part because the exact species of the consumer and consumed is not known. When members of the same species commonly eat each other, it is considered cannibalism, but if a hominin species occasionally devours the flesh of its own species or close relatives, it is categorized as part of a broader practice called “anthropophagy.”

KNM-ER 741, which was initially discovered in 1970 by the paleoanthropologist Mary Leakey, has been interpreted as belonging to either Australopithecus boisei or Homo erectus, but ultimately its exact identity remains a mystery. It’s also not clear which hominin species made the butchery marks, so this is not a clear-cut case of cannibalism, though it is tantalizing evidence of anthropophagy.

“Given the variability in lion behavior and the presence of both cut marks and tooth marks on the fossil hominin tibia, it is not possible to infer the cause of death of the individual, or even the primary consumer,” the team said in the study. “However, the location of the cut marks on the posterior tibia shaft suggests that flesh was likely on the carcass at the time that the cut marks were inflicted.”

In other words, a predatory cat may have feasted on this hominin’s body 1.45 million years ago, only to be scared off by hominins who finished the meal themselves. Conversely, the marks may have been inflicted in the opposite order, with hominins butchering the hominin first and a cat later scavenging the remains of the carcass. 

While the full story of these gruesome marks will probably never be known, this unprecedented evidence of ancient butchery sheds new light on the world inhabited by our human precursors in the deep past. It is also a valuable reminder that many discoveries can be made by revisiting known specimens in museum collections, in addition to looking for new fossils in the field.  

“Going back into museum collections, reexamining other hominin fossils, and finding butchery marks on other hominin fossils could help us determine how common this behavior was,” Pobiner concluded.  “I think studying the marks on the Stw 53 skull using the same methods as we used in this paper would be a great way to build on this study.”